A young man was scalped and killed by the blades of a model remote-controlled helicopter that chopped off the top of his head in Gravesend, Brooklyn today, sources said.

The 19-year-old victim  a well-known model helicopter enthusiast  was on the corner of Shore Parkway and Bay 44th Street around 3:40 p.m., when he lost control of the toy aircraft, it boomeranged and sliced off the top of his head

I’m not buying it. RC copters aren’t that heavy, the blades shouldn’t have nearly enough inertia to get through bone. Could hit in just the wrong place and get killed that way, but not an actual head chopping.

10
posted on 09/05/2013 2:40:02 PM PDT
by discostu
(This is why we have ants!)

Has Bloomberg come out with an ordinance that requires all RC aircraft operators, spectators and innocent passerby’s to wear football helmets? 100% background checks for purchasers of RC aircraft with a 1,000 hour training and license certification?

30
posted on 09/05/2013 3:06:00 PM PDT
by RetiredTexasVet
(Progressives are never accountable for "unintended consequences" .... just for causing most)

Im not buying it. RC copters arent that heavy, the blades shouldnt have nearly enough inertia to get through bone.

I agree. The rotary WING of an RC helicopter is a fragile thing. It does not have a cutting edge (rather rounded it is) and is not made of anything as tough as a pen knife blade.

I say cause of death was blunt force trauma with an ancillary skimming off of the scalp...which would have bled like a sumbitch. Skull bone is a lot tougher than the rotor of an RC rotary wing aircraft.

RC copters arent that heavy, the blades shouldnt have nearly enough inertia to get through bone.

Maybe not all the way through a large bone, but... A friend's 3XXmm rotor span indoor electric heli with flexible non-weighted plastic blades fractured his index finger. The heli's all-up weight is 300-some grams.

Now try an 700-900 class outdoor heli (I have not looked into the type of machine involved in today's mishap -- could have been small as a 450.

From an RC forum:

In the "Battle Axe" thread we saw what a 900 can do to a tree , assuming the head rpm was over 1500 rpm putting the tipspeed somewhere around 400mph. 400mph seems to be a magic number regarding tip speed on most 3d style helis today

700mm-800mm blades will cut to the bone at 900 rpm just as easily as at 1800. There's more than one injury thread starting off with "while the rotors were spooling down" or "after it had lost most of its headspeed".

the problem isn't that the heads are being operated at some unsafe speed and the problem cannot be fixed by reducing to a "safe" RPM.

The reason these are dangerous is because a rotor with the properties that allow it to efficiently cut through air and rapidly provide large amounts of force to the main shaft without failing also allow it to transfer large amounts of energy and efficiently cut through living tissue.

really, the problem is we are dealing with high-energy machines because to get them to perform the way people want them to perform requires high amounts of energy.

a little math:

using the values on the EDGE website for their 800 mm rotor, we have a mass of 270 grams. center of mass position is not indicated, but i'm going to assume it's around 2/3 (if someone knows better, feel free to tell me) at 600mm. this means that at 900 rpm, the center of mass will have a linear velocity of roughly 30 m/s.

if we assume worst case scenario, blade hits limb and is stopped dead, we can assume roughly 1/10 second to stop, which give us a deceleration rate of 300 m/s/s. using F=ma we have 0.27kg*300 = 81 newtons of force.

if we assume frontal area of the blade as it makes contact at 1/10=in wide (and this is a generous estimate, i would not be surprised if the effective contact was much thinner) along, say, 3" wide piece of forearm, that gives us a total contact area of 0.3 inches, for an impact pressure of roughly 270 psi.

Now, i was not able to find a solid number, but most sources indicate that as little as 100 psi can break the skin, and the tissues beneath require less force once skin has been broken. so the initial impact give us almost triple the skin-penetration requirement, and then the second blade come swinging around and adds another 80 lbs of impact to the mix... and this is at the "low" headspeed of 900 rpm as in the above video, and using very conservative figures for the math.

basically, it boils down to what i mentioned above, if you want to toss a 2-3kg machine around at 3-4Gs of acceleration, you are going to necessarily involve a large amount of force to do it. the interface which transfers that force into the air will just as happily transfer it into a person if a person ends up in the way.

49
posted on 09/05/2013 3:28:57 PM PDT
by steve86
(Some things aren't really true but you wouldn't be half surprised if they were.)

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